Body implantable electrical leads for the delivery of stimulation energy to a desired body site are known to the prior art. Recent years have seen increased usage of transvenous leads which can deliver the stimulation energy to the desired body site while significantly lowering patient risk and morbidity. For example, the use of a transvenous/endocardial lead eliminates the necessity of a thoracotomy while delivering stimulation energy to the heart to provide a pacemaking function. Such endocardial leads may be used for sensing as well as pacing.
In many stimulation and sensing contexts, maintenance of a reliable electrical contact at the desired electrode site has proven difficult. To overcome this in the endocardial pacemaking environment, for example, pliant tines have been positioned adjacent the lead electrode to interact with cardiac structure to maintain the electrode in electrical contact with the heart tissue while allowing a removal of the electrode should that prove necessary, for repositioning, for example. An example of such tines employed for this purpose is disclosed in U.S. Pat. No. 3,902,501 issued Sept. 2, 1975, to Paul Citron and Eugene A. Dickhudt for ENDOCARDIAL ELECTRODE, which patent is commonly owned with the present invention and which is hereby incorporated herein by reference. In the incorporated patent, a plurality of tines extend from the lead body adjacent the tip and form an acute angle with the electrode body to cooperate with heart structure, particularly the trabeculae found in the right ventricle and atrial appendage, to maintain the electrode in position. The tines are disclosed as being pliant and non-conductive and serve the stated purpose of maintaining an electrode tip in electrical contact with heart tissue while allowing a removal of the electrode should that prove necessary. The tines are stated as making any angle with the lead body with an angle of approximately 45.degree. maintaining the necessary electrical contact in a very efficient manner. Polyurethane is disclosed as a pliant material from which the tines may be formed while the catheter/conductor combination (lead body) is stated as being desirably as flexible as possible. However, no relationship is specified between the flexibility/stiffness of the tines relative to the flexibility/stiffness of the lead body.
Further examples of tined leads are disclosed in U.S. Pat. Nos. 3,939,843 issued Feb. 24, 1976, to Nicholas P. D. Smyth for TRANSVENOUS ELECTRODE and U.S. Pat. No. 4,003,357 issued July 5, 1977, to John R. Helland and Kenneth B. Stokes for NON-FIBROSING CARDIAC ELECTRODE, both of which are commonly owned with the present invention and which are hereby incorporated herein by reference. The Smyth patent discloses the use of polyurethane for the lead body insulating member and tines while the Helland et al patent discusses the superior elastomeric properties of a particular urethane relative to silicone rubber, a commonly used prior art lead body insulating member. However, neither of the latter incorporated patents disclose a stiffness/flexibility relationship between the tines and lead body that would optimize the holding power of the tines to facilitate lead removal for repositioning.